1. Field of the Invention
The present invention relates to power management in a redundant power system. More particularly, the present invention relates to a power management scheme in a redundant power system where more than one redundant power supplies are available to a power bus. Particular utility for the present invention is power management for the IBM Tape Library System such as described in U.S. Pat. No. 6,356,803; the present invention has general applicability to any high-reliability system that utilizes multiple redundant power subsystems.
2. Description of Related Art
Many high reliability systems require redundant power to permit the system to continue normal operations in the event of a power subsystem failure. A common approach involves a technique called N+1, where N is the number of required power subsystems (based on the power demands of the system) and the +1 indicates that there is a single back up power subsystem. While this methodology is convenient for some designs, there are cases where more than one back up power system may be desired, or even required.
Certain problems are associated with power subsystems that involve more redundancy than N+1. For example, the power must be dynamically managed to ensure that too much power is not placed on the power bus (which can create a serious safety hazard). System complexity further increases when the power subsystems are located apart from each other. In order to effectively manage power under these conditions, a communication channel must be established between power subsystems. However, communication channels are equally susceptible to failure, and/or loss of connectivity between the power nodes. Thus, there is a need for power management in a redundant power system that eliminates or reduces single points of failure and maintains safe levels of power on the power bus.
Accordingly, the present invention provides power management for multiple redundant power supplies in an N+M system, where N represents the minimum number of power subsystems required to power all the subsystems and M represents the number of redundant power supplies available (M greater than 1). During reset periods of one or more of the power subsystems, the present invention permits autonomous control of the individual power subsystems to couple a power supply to a power bus (if power is required) based on the power condition of the power bus. During normal operation, the present invention provides global control over the operating conditions of each of the power subsystems to ensure that a predetermined number of redundant power supplies are coupled to the power bus.
In one exemplary embodiment, the present invention provides a redundant power supply management system that includes a plurality of power subsystems each comprising a power supply and a controller for controlling the activation of each power supply, a power bus coupled to each power supply, a master controller, and a communications bus coupled to-said power subsystem and the master controller. Further, during a reset period of the power subsystem, each controller is adapted to monitor the power state of the power bus and couple a power supply to the power bus if the power bus requires power, thereby ensuring a minimum of one power supply connected to the power bus. Additionally, the master controller is adapted to monitor the power subsystems and couple a predetermined number of power supplies to the power bus, thereby ensuring a number of redundant power supplies available to the power subsystems.
In another exemplary embodiment, the present invention provides a system for controlling a plurality of power supplies in a redundant system that includes a plurality of power supplies selectively coupled to a common power bus, a controller associated with each power supply for sending commands to each power supply, and a master controller coupled to each power supply for sending commands to each power supply. The controller is operable during a reset period to command the power supply to couple to the power bus if the power bus requires power. The master controller is operable during periods other than said reset period to couple a predetermined number of power supplies to the power bus based on status information received from the power supplies.
In preferred embodiments, the master controller is further adapted to monitor each said power subsystem to determine which said power subsystems fail to communicate with said master controller, and upon such failure, said master controller further adapted to determine the number of power subsystems that confirm to be supplying power to said power bus, and if the sum of said failed subsystems and said confirmed subsystems is less than a predetermined number, said master controller instructing an additional power subsystem to couple a power supply to said power bus.
Also in preferred embodiments, the controller is adapted to control the activation of said power supply only during a reset or power-on period of said power subsystem, wherein said master controller adapted to control the activation of each said power supply at all other times other than said reset or power-on period. Preferably, each said power subsystem has a unique identification number, and a delay time based on said unique identification number. For example, the delay time can be defined as: Delay(sec)=2 (power subsystem numberxe2x88x921).
The present invention also provides an exemplary method for managing multiple redundant power supplies, comprising the steps of:
controlling a plurality of power supplies to selectively couple each said power supply to a power bus to supply power;
during a reset period for each said power supply, the step of controlling further comprising the step of coupling said power supply to said power bus if said power bus requires power; and
during time periods other than said reset period, the step of controlling further comprising the step of coupling a predefined number of said power supplies to said power bus.